A former inmate pleaded not guilty Wednesday to forcing two teens into prostitution with the help of his girlfriend, who was a guard at the western Pennsylvania prison where he served time for drug charges.

Rasul Abernathy, 32, appeared before a federal magistrate in Pittsburgh on charges of conspiracy to engage in sex trafficking and two counts of sex trafficking of a child -- a 16-year-old girl and a 17-year-old boy.

Abernathy is charged along with his former guard, 34-year-old Poshauntaramin Walker, who pleaded not guilty last week. Her public defender declined to comment.

Abernathy's attorney, Douglas Sughrue, hopes to convince a jury that Abernathy was simply trying to help "young people whose lives aren't well off, who were looking for people to help them through rough times."

"We will allow a jury to decide between two interpretations of facts, one that favors the government and one that favors the defense," Sughrue said.

Details of the charges are spelled out in an FBI search warrant unsealed in February, a few days after the couple was arrested in Philadelphia.

Abernathy met Walker when he was incarcerated from February 2007 to September 2008 at the state prison in Greensburg, about 30 miles east of Pittsburgh.

After Abernathy's release, the couple wound up in North Versailles, a Pittsburgh suburb, where Abernathy met the 16-year-old after she ran away from a court-ordered juvenile placement.

Abernathy told the girl she could live with Walker, but he didn't tell her that he lived there, too, and they'd all have to share one bed, authorities said. About a month later, the couple began prostituting the girl by posting online ads with her picture, the FBI affidavit said.

Authorities allege the girl was prostituted from July 2012 to March 2013, while the boy was trafficked from December 2012 to March 2013. Few details of the allegations involving the boy are included in the court documents.

According to the search warrant, Walker showed the girl how to dress and apply makeup, and Abernathy told her what to charge for sexual services. The couple gave her marijuana and pain pills to relax her before trysts -- and alcohol afterward -- and physically abused her if she refused to provide sexual services or tried to run away, authorities said.

The FBI also alleges that a former inmate friend of Abernathy's raped the girl, and Abernathy told her it was a "learning experience."

That man, Solomon Owens, 36, has been jailed and was ordered to stand trial on rape and other charges after a preliminary hearing last month.

Walker and Abernathy also face related charges in state court. Walker last month was ordered to stand trial on charges of interfering with the custody of a minor, furnishing alcohol to a minor and corruption of minors. Abernathy faces a preliminary hearing Thursday on charges including involuntary deviate sexual intercourse, corruption of minors and sexual assault.

50 Photos: The facts of Pa. prison life

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This slideshow takes a look at the prison and jail system in Pennsylvania, who's in it, what it costs and how the state's system compares to the rest of the country.